1. Field of the Invention
This invention relates in general to document processing apparatus and more particularly to such apparatus that detect magnetic characters on documents.
2. Description of the Prior Art
Document processing apparatus often must detect magnetic characters on the documents they process. U.S. patent application Ser. No. 573,787 of Templeton and assigned to common assignee describes such an apparatus. The disclosed apparatus first orientates the magnetic dipoles of the characters in a predetermined fashion using a writing device and then detects the magnetic characters using a reading device.
One type of magnetic character detection apparatus detects characters that have been DC (unidirectionally) magnetized, that is the magnetic dipoles of the characters are aligned pointing in one general direction. Such magnetization has been accomplished utilizing a writing device located on only one side of the document transport path. Such device includes a U-shaped magnet having opposite magnetic poles on its legs. Magnetizable material extends from each leg toward the other leg and slightly above the open end of the U to form pole tips which are separated from each other by a small air gap, such as 0.08 mm. The document having magnetic characters thereon is moved adjacent to and past the gap. The magnetic characters are spaced from the pole tips and gap by a layer of non-magnetic material with a piece of resilient non-magnetic material extending from the other side of the transport path holding the document against the layer of non-magnetic material covering the pole tips and gap. Leaking flux in the vicinity of the air gap between the pole tips attempts to orientate the magnetic dipoles as the document passes thereby.